Hydro balance

[Gary]

Anyone have a basic of where the balance point should be on a 32 inch hydro.I am at 50/50 now but i dont think its right. Thanks

[Heath M]

1 - 2 inches behind the sponsons

Heath

[JimClark]

as close as .75 inches aft of the back of the sponson

[sporthydrofan]

Hey guys new to the forum. Building a 32" sport hydro with a 580L and 5S x445 prop. im having problems keeping the boat from hopping up in the air once it hits 40mph+ range. The strut angle is 0 and the shaft is about 1" from the bottom... so i dont think that is the issue. The boat seams to be very light perhaps its getting too much lift, what is the ideal weight and COG for a 32" sport hydro trying to go 55-60 mph?

[Hydromaniac]

The cog placement is not a hard rule, The fastest sport hydro I have built would run and was clocked at just under 70 mph on 4s. It was a 32 inch vintage hydo. The cog at over 50mph had to be moved way forward to 1 1/2 inches ahead of the sponson transome to keep the nose down at full speed, Sometimes you need to play with weight placement to get her to run and stay on the water at higher speeds.

[egneg]

I know it's not a hydro but my XS2 has the CG at the back of the sponsons. It still blows over at 60+ MPH even though I have all the weight as far forward as I can get it.

[Jeepers]

Its not what is right it is a matter of what works and what you want the hydro to do, I never build to the one inch behind the sponson rule. because weight and power are gonna be a huge factor test the boat on the set up you have and see what happens. TEST & TUNE TEST& TUNE!!!!!!!!

[sporthydrofan]

The cog placement is not a hard rule, The fastest sport hydro I have built would run and was clocked at just under 70 mph on 4s. It was a 32 inch vintage hydo. The cog at over 50mph had to be moved way forward to 1 1/2 inches ahead of the sponson transome to keep the nose down at full speed, Sometimes you need to play with weight placement to get her to run and stay on the water at higher speeds.

Just under 70mph on 4S .. what motor and prop did you use?
did you use 2 batteries?
Im only using a single 5S 5amp battery, should i use 2 to weigh it down more?

my COG is about 50% of the length of the boat... i didnt want to move it to far foward because i was worried it will nose dive since it hops so much... i did put a zip lock sandwitch bag full of sand under the cowl seems like 1.5 lbs and the hopping was reduced a great deal. im thinking of buying some automotive rim lead weights and sticking them in the hull to weigh it down a bit. just testing now the min amount of weight that it will take to eliminate the hopping at higher speeds.

I would really love to achieve that 65-70 mph mark. Im not racing the boat or anything but id like it to do laps at my pond and smoke all the other guys that have those stock UL-1 RTR's without blowing over...

right now it wont go WOP because it hops and almost blows over right around 40

[m4a1usr]

What hull, what motor, what hardware, what prop? You might be running a high lift prop, you might have the strut set too low, etc. Too many variables to give you an accurate answer. Information you have provided is too vague.

John

[sporthydrofan]

Hey guys new to the forum. Building a 32" sport hydro with a 580L and 5S x445 prop. im having problems keeping the boat from hopping up in the air once it hits 40mph+ range. The strut angle is 0 and the shaft is about 1" from the bottom... so i don't think that is the issue. The boat seams to be very light perhaps its getting too much lift, what is the ideal weight and COG for a 32" sport hydro trying to go 55-60 mph?

my original question above ...

Octura x445 prop that is..


the hull is an Asian brand not sure what brand it is, I picked it up on craigs list for 100 bux. it is a very nice quality construction very sturdy fiberglass, not sure what else to say about it. I'm new to the FE scene but it is probably a copy of a aquacraft or proboats.. hope that helps..

[domwilson]

Welcome to the forum. Can you post pics of your hydro and the hardware setup?
We may be able to help you.

[Simon.O.]

I know you are after the CG or balance point for your hull.
There are many factors that can affect how a hydro will perform even with the perfect prop and power combination.
Strut height and angle will determine the running attitude and indeed the AoA of the front sponsons.
Is the front or rear hopping or is it the whole hull.

I ask as I went through a lot of changes to one of my old 26" hydros and after weeks of trial and mostly error it was determined that I needed more weight overall.
Even now on the odd occasion that I run that hull it will clear 40mph but that is it. Any more will blow it off regardless of setup or weight (within reason) The design is fine for that speed and no more.

Back to your hull.
Can you shoot up some pics. Take the turn fin off and lay it on a table so that the sponsons and strut are on the table. Shoot a pic from the front, side and rear.
A close up of the sponson profile may help too.
There are plenty of very experienced hydro runners here (not me) and they can help a lot.
I may do another hydro but it will naturally be a weird design like most of my other hulls.

[sporthydrofan]

dont have my camera with me, i can take some shots tomorrow and post em.. but in the mean time any rules of thumb .. I got from someone here that goes 70 mph his COG is past the sponson transom ... i think my issue is overall weight it is getting too much lift at ~40 mph and hoping around alot !

[sporthydrofan]

the front is hopping.. at about 25 mph than the whole hull hops at about 35-40 and get 8-10 inches of air!! sometimes it lands fine sometime one of the sponsons goes in first and then dive under and puts it to a complete stop... not good for the cowl...!

AOA is angle of attack... what should it be?

[m4a1usr]

dont have my camera with me, i can take some shots tomorrow and post em.. but in the mean time any rules of thumb .. I got from someone here that goes 70 mph his COG is past the sponson transom ... i think my issue is overall weight it is getting too much lift at ~40 mph and hoping around alot !

Sorry, I didnt read the entire thread. You did give some relative details. Get rid of the transom hopping first. If the hull comes up on plane with few issues then focus on that problem. A 1" deep strut and a 445 prop should be fine to begin with. Angle the strut down to reduce the lift. That means the prop nut up and the strut nose piece down in case that doesnt make sense. Once the hopping is gone get busy with your COB. And it could end up forward or aft of the turn fin.

John